I was right all those years ago, the charge has little or nothing to do with friction. Speed of impact, temperature, and size of ice crystals or particulates are what causes the charge build up. Would you agree the charge build up is due to different work functions or not?
I might have agreed to that prior to reading the paper I have referenced in my last post, but not after having read through it in some detail.
I do agree that in the usual case of contact charging, charges are exchanged between the objects in proportion to the difference between the effective work functions associated with the two (different) materials.
However, in the thunderstorm cloud, we are talking about a mixture of a materials, ascending ice crystals and descending graupel; both forms of the same fundamental substance H2O, and therefore they must have nearly the same chemical composition and presumably the same value of effective work function.
This paper argues that there is an “unusual property of charging during ice-ice collisions” which arises “from a primarily one-way transfer of charged melt” which differs from the usual case of contact charging.
The authors claim during a net transfer of electric charge in ice-ice collisions, there is “mass and charge transfer from the corner of a facetted crystal to the underside of sublimating graupel”
When an ice crystal lattice is formed, H2O undergoes a proton shift along a hydrogen bond, creating -OH and +H3O ions and “the effective charge of OH− in ice, qOH, is charge −0.62e, not e” (I am not 100% clear on why the effective charge is −0.62e, and not e. I need to read up on that but it is suggestive of something to do with time constants)
So, before the collision with the graupel, the crystal surface has OH− charge. “The collision squeezes this charged mass into melt on the underside of the graupel, that is pushed outward from a thin region between the ice particles and then freezes onto the graupel”
Bottom line is the mass transfer from crystal to graupel also transfers some electric charge to the graupel.
The rest of the paper goes into detail about the other variables involved such as temperature and collision velocity, with all the relevant mathematics. It is all interesting, depending on how deep you want to delve into it and how much more time you need to spend in lockdown.
I agree, Lightning does happen at different times of day, other than just after sunset near the equator. What I observed crossing the Atlantic, Pacific and Indian Oceans is that almost without fail cumulus builds during the day, and the lightning starts just after it gets dark. It is usually is over in about 2-3 hours, when the clouds all usually disperse leaving the sky clear and full of stars, unless there is bad weather
I too, have sailed the oceans blue, and have experienced many lightning and thunder storms mostly around mid-day in the tropics. Lightning is most pronounced at night, for obvious reasons, but anecdotally at least, I don't believe it happens more frequently at night.